Preheat oven to 350˚F.
Line a 9x13 baking dish with parchment paper with an overhang on the sides so it’s easier to pull out the baked bars. Set aside.
Using an electric mixer, cream together the butter and sugar for 2 to 3 minutes, or until light and fluffy.
Add vanilla and salt; beat just until combined.
Add flour, about ¼-cup at a time, and continue to beat until completely combined.
Transfer dough to previously prepared baking dish; spread it out and press on top to flatten.
Bake the crust for 20 to 23 minutes, or until lightly golden on top.
Remove from oven and set aside to cool for about 30 minutes.
In the meantime, work on the filling:
Combine sugar, flour, eggs, and lemon juice in a large mixing bowl; whisk together until thoroughly incorporated and well combined.
Pour the filling over the previously baked crust.
Return to the oven and bake for 23 to 25 minutes, or until firm.
Remove from oven and let cool for 1 hour at room temperature.
Refrigerate for 3 to 4 hours, or until chilled. They are best if chilled overnight.
Once cool, lift up by the parchment paper and transfer to a cutting board.
Using a sharp knife, cut into 16 bars.
Garnish with powdered sugar and lemon slices.
Cover and store in the fridge for up to a week.